Process for producing ε-caprolactam

ABSTRACT

The present invention provides a method for producing ε-caprolactam which comprises the step of treating, with water, a reaction product containing 1-aza-2-alkoxy-1-cycloheptene, which is obtained by gas phase Beckmann rearrangement reaction of cyclohexanone oxime using a solid catalyst in the presence of alcohol, to eliminate the 1-aza-2-alkoxy-1-cycloheptene. The resulting ε-caprolactam usually has a 1-aza-2-alkoxy-1-cycloheptene content of 100 ppm or less, preferably 25 ppm or less, more preferably 10 ppm or less and, therefore, has low free basicity and good qualities.

This application is the national phase under 35 U.S.C. §371 of PCTInternational Application No. PCT/JP99/02115 which has an Internationalfiling date of Apr. 21, 1999, which designated the United States ofAmerica.

FIELD OF THE INVENTION

The present invention relates to a method for producing ε-caprolactamhaving low free basicity. Specifically, the present invention relates toa method for producing ε-caprolactam having low free basicity whichcomprises a step of producing ε-caprolactam by a gas phase Beckmannrearrangement reaction of cyclohexanone oxime using a solid catalyst inthe presence of alcohol.

BACKGROUND OF THE INVENTION

ε-caprolactam is an important compound as an intermediate in producingnylon-6. A method for producing ε-caprolactam from cyclohexanone oximeby gas phase Beckmann rearrangement reaction using a solid catalyst isknown, and as the solid catalyst, it is known to use a boron-basedcatalyst, silica-alumina catalyst, solid phosphoric acid catalyst,complex metal oxide catalyst, zeolite-based catalyst and the like.Further, Japanese Patent Application Laid-Open (JP-A) Nos. 62-123167 and63-54358 show examples using a high-silica type metallosilicatecatalyst, and the selectivity in gas phase Beckmann rearrangementreaction of cyclohexanone oxime using such a catalyst system has beenfairly improved as compared with conventional catalyst systems. JP-A No.2-275850 discloses that the selectivity is further improved in a methodfor producing ε-caprolactam in which a lower alcohol is allowed to existtogether with a solid catalyst. Moreover, JP-A 5-201965 discloses thatthe selectivity and catalyst life are improved when ε-caprolactam isproduced by gas phase catalytic reaction of cyclohexanone oxime inallowing water to exist in the reaction system using a zeolite catalystin the presence of alcohol and/or ether compound.

On the other hand, it is known that by allowing an alkylating agent suchas dimethyl sulfate and diazomethane to act on ε-caprolactam, acorresponding 1-aza-2-alkoxy-1-cycloheptene (hereinafter, sometimesabbreviated as AAH) is synthesized. However, it is not known at all thatAAH is generated as a by-product in gas phase Beckmann rearrangementreaction of an oxime in the presence of alcohol, and that one ofstandards for the product, free basicity, may sometimes not be satisfiedwhen AAH remains in the product, ε-caprolactam. The standard in freebasicity varies depending on every user and is not restricted. It isrequired that the product usually have free basicity of about 1 meq/kgor less, preferably about 0.3 meq/kg or less, more preferably about 0.1meq/kg or less. It is known that when free basicity in the product,ε-caprolactam, is high, reverse influence is exerted in polymerizationto a nylon.

SUMMARY OF THE INVENTION

Under such circumstances, the present inventors have intensively studiedto find an industrially advantageous method for producing ε-caprolactamhaving low free basicity and providing high yield. As a result, thepresent inventors have found that when ε-caprolactam is obtained by gasphase Beckman rearrangement reaction using a solid catalyst in thepresence of alcohol with using cyclohexanone oxime as a raw material,AAH is usually produced and present in the reaction product in aselectivity of from about 0.1% to about 10% depending on the reactionconditions, and that when the AAH is contained in ε-caprolactam, thepresence of the AAH causes to enhance free basicity and reduce qualitiesof the product, and that when the reaction product is treated withwater, the free basicity is reduced and yield of ε-caprolactam isincreased due to conversion of the AAH with water into ε-caprolactam,completing the present invention.

First, the present invention provides a method for producingε-caprolactam which comprises the step of treating, with water, areaction product containing 1-aza-2-alkoxy-1-cycloheptene, which isobtained by gas phase Beckmann rearrangement reaction of cyclohexanoneoxime using a solid catalyst in the presence of alcohol, to eliminatethe 1-aza-2-alkoxy-1-cycloheptene.

Secondly, the present invention provides a method for producingε-caprolactam which comprises the steps of separating a componentcomprising 1-aza-2-alkoxy-1-cycloheptene from a reaction productcontaining 1-aza-2-alkoxy-1-cycloheptene obtained by gas phase Beckmannrearrangement reaction of cyclohexanone oxime using a solid catalyst inthe presence of alcohol, and treating the separated component comprising1-aza-2-alkoxy-1-cycloheptene with water to eliminate the1-aza-2-alkoxy-1-cycloheptene.

Thirdly, the present invention provides a method for producingε-caprolactam according to the above first-described method, wherein thereaction product to be treated with water is a reaction product obtainedby substantially separating an alcohol.

Fourthly, the present invention provides a method for producingε-caprolactam according to the above secondly-described method, whereinthe reaction product to be used for separating the component containing1-aza-2-alkoxy-1-cycloheptene is a reaction product obtained bysubstantially separating an alcohol.

Fifthly, the present invention provides a method for producingε-caprolactam, which comprises the steps of separating a componentcontaining 1-aza-2-alkoxy-1-cycloheptene from a reaction productcontaining 1-aza-2-alkoxy-1-cycloheptene obtained by gas phase Beckmannrearrangement reaction of cyclohexanone oxime using a solid catalyst inthe presence of alcohol, treating the separated component containing1-aza-2-alkoxy-1-cycloheptene with water to convert the1-aza-2-alkoxy-1-cycloheptene into ε-caprolactam, and put the resultingproduct into a step prior to the step of separating the componentcontaining 1-aza-2-alkoxy-1-cycloheptene from the gas phase Beckmannrearrangement reaction product.

Sixthly, the present invention provides a method for producingε-caprolactam according to the above fifthly-described method, whereinthe reaction product to be used for separating the component containing1-aza-2-alkoxy-1-cycloheptene is a reaction product obtained bysubstantially separating an alcohol.

Seventhly, the present invention provides a method for producingε-caprolactam by gas phase Beckmann rearrangement reaction ofcyclohexanone oxime using a solid catalyst in the presence of alcohol,which comprises the step of treating 1-aza-2-alkoxy-1-cycloheptenegenerated as a by-product with water so that a1-aza-2-alkoxy-1-cycloheptene content in the ε-caprolactam is 100 ppm orless.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

ε-Caprolactam in the present invention usually has an AAH content ofabout 100 ppm or less, preferably about 25 ppm or less, more preferablyabout 10 ppm or less, and has low free basicity and has excellentqualities.

The ε-caprolactam in the present invention having such physicalproperties can be produced by, for example, a method in which a reactionproduct containing AAH obtained by allowing cyclohexanone oxime to reactunder gas phase reaction conditions using a solid catalyst in thepresence of alcohol is treated with water, or preferably a reactionproduct containing AAH obtained by substantially separating an alcoholfrom the above-described reaction product is treated with water, or amethod in which a component mainly containing AAH is further separatedfrom the reaction product by distillation or the like and then thecomponent is treated with water. By such a water treatment, AAH isconverted into ε-caprolactam so that ε-caprolactam having a small AAHcontent can be obtained.

In the above-described methods, silicon-oxide-containing catalysts,preferably crystalline metallosilicates may be used as the solidcatalyst. In particular, it is more preferred to use crystallinemetallosilicates having a Si/Me atomic ratio of 500 or more (wherein Merepresents one or more metal elements selected from Al, Ga, Fe, B, Zn,Cr, Be, Co, La, Ge, Ti, Zr, Hf, V, Ni, Sb, Bi, Cu, Nb and the like).Also, it is more preferred to use a crystalline silicate composed ofsilicon dioxide containing substantially no Me component. The Si/Meatomic ratio can be measured by commonly-used analysis means, forexample, an atomic absorption method, a fluorescent X-ray method and thelike. These catalysts can be produced by known methods. The crystallinemetallosilicate and crystalline silicate are known to include variouscrystalline types, and those having so-called pentasyl structure arepreferred.

In the production of ε-caprolactam, a lower alcohol may usually be usedas the alcohol to be allowed to exist in the reaction system. Examplesof the lower alcohol include alcohol having 6 or less carbon atoms, andspecifically, one or more kinds of alcohol selected from methanol,ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, n-amyl alcoholand n-hexanol. Particularly, it is preferred to use one or more kinds ofalcohol selected from methanol, ethanol, n-propanol, isopropanol andn-butanol since remarkable effects are manifested in improvement ofselectivity to ε-caprolactam and catalyst life. Among them, methanol andethanol manifest remarkable effects and, therefore, these areparticularly preferred in the industrial point of view.

Further, water can also be used together with alcohol in theabove-described production of ε-caprolactam. The amount of water to beused is 0.06 to 2.5 times, preferably 0.18 to 1.9 times in terms ofmolar ratio based on 1 mol of cyclohexanone oxime. The ratio out of thisrange tends to cause large decrease of catalyst activity. Use ofsuitable amount of water exhibits effect for improving catalyst life.

The reaction may usually be effected under a pressure of 3 atm or lower.The reaction can also be effected under reduced pressure lower thanatmospheric pressure. The reaction may be conducted as a common gasphase catalytic reaction in fixed bed mode or fluidized bed mode.Cyclohexanone oxime as the raw material reacts in a catalyst layer ingaseous phase, and alcohol may be previously mixed with thecyclohexanone oxime or also be supplied to a reaction vessel separatelyfrom cyclohexanone oxime. In the case of the fixed bed reaction, it ispreferred that cyclohexanone and alcohol are sufficiently mixed and passthrough the catalyst layer in such a mixed condition. In the case of thefluidized bed reaction, it is not necessarily required thatcyclohexanone oxime and alcohol are previously mixed. They can besupplied separately, and alcohol can also be divided and then added.Alternatively, in the case of the fluidized bed reaction, alcohol mayalso be added at an upper flow side than cyclohexanone oxime.

Water may also previously be mixed with cyclohexanone oxide and suppliedto a reaction vessel, or may also be supplied separately fromcyclohexanone oxime. In the case of the fluidized bed reaction, it canbe divided and then added.

The amount of alcohol to be allowed to exist in the reaction system maybe suitably from 0.1 to 20 times, preferably 10 times or less, and mostpreferably from 0.3 to 8 times in terms of ratio by weight based oncyclohexanone oxime.

In the reaction system, a compound inactive in the reaction such asbenzene, cyclohexane and toluene, or an inert gas such as nitrogen mayalso be allowed to exist as a dilution gas.

The reaction temperature may usually be from about 250° C. to about 500°C., preferably from about 300° C. to about 450° C., more preferably fromabout 300° C. to about 400° C. The space velocity (WHSV) ofcyclohexanone oxime as the raw material is from about 0.1 to about 40hr⁻¹ (namely, the rate of supplying cyclohexanone oxime per 1 kg of acatalyst is from about 0.1 to about 40 kg/hr). It is selected in therange preferably of from about 0.2 to about 20 hr⁻¹, more preferablyfrom about 0.5 to about 10 hr⁻¹.

One of the embodiments of the present invention is that a reactionproduct containing AAH is treated with water under specific conditionswherein the reaction product is obtained by gas phase Beckmannrearrangement reaction of cyclohexanone oxime conducted in the presenceof alcohol, and that AAH contained in a reaction product obtained bysubstantially separating an alcohol beforehand by distillation or thelike from the above-described reaction product is treated with waterunder specific conditions.

Another embodiment of the present invention is that an AAH-condensedfraction and ε-caprolactam having an AAH content of, usually, 100 ppm orless, preferably about 25 ppm or less, more preferably about 10 ppm orless are separated from each other by distillation from a reactionproduct itself obtained by gas phase Beckmann rearrangement reaction orfrom a reaction product obtained by separating an alcohol from theabove-described reaction product, and then the AAH-condensed fraction istreated with water under specific conditions. The AAH-condensed fractionmay contain ε-caprolactam, a by-product having a low boiling point andwater. In such a case that the AAH-condensed fraction is previouslyseparated by distillation and then is treated with water, it ispreferred that a treated liquid obtained after the water treatment isused and recycled in a step prior to a step of distillation forcondensing AAH since a small amount of by-products other thanε-caprolactam as well as ε-caprolactam itself may be contained in thereaction product obtained after the water treatment. This method isespecially recommended since there is no need to add a new facility andthe existing facilities can be utilized to effectively eliminateby-products made in the water treatment of AAH and effectively recoverε-caprolactam produced by conversion of AAH.

In the above-described gas phase Beckmann rearrangement reaction, AAH isproduced in a selectivity usually of from about 0.1% to about 10% as aby-product in the reaction, and is contained in the reaction product.The kind of AAH is different depending on the kind of alcohol utilizedin the rearrangement reaction. For example, when methanol is utilized asthe alcohol, 1-aza-2-methoxy-1-cycloheptene is produced, when ethanol isutilized, 1-aza-2-ethoxy-1-cycloheptene is produced, and when n-propanolis utilized, 1-aza-2-n-propoxy-1-cycloheptene is produced. The reactionproduct of gas phase Beckmann rearrangement reaction containing1-aza-2-alkoxy-1-cycloheptene as a by-product or the componentcontaining 1-aza-2-alkoxy-1-cycloheptene separated from the reactionproduct is treated with water and the AAH is hydrolyzed and convertedinto ε-caprolactam to consume the AAH. When AAH exists in ε-caprolactamin a specific concentration or more, free basicity as one of productstandards of ε-caprolactam deteriorates.

In the present invention, when the reaction product containing AAH andε-caprolactam obtained by the above-described reaction is treated withwater, the AAH is eliminated and the yield of ε-caprolactam increases,since ε-caprolactam is produced from the AAH. It is preferred that atreated liquid obtained after the water treatment is used and recycledin a step prior to a step of separating alcohol since, due to the watertreatment, AAH mainly produce ε-caprolactam and a corresponding alcohol.

The amount of water used in the water treatment may be from about 1equivalent to about 50 equivalent, preferably from about 3 equivalent toabout 30 equivalent to the amount of AAH existing in the reactionsystem. When the amount of water is less than 1 equivalent,decomposition of AAH is not sufficient. When the water is too much, thewater needs to be removed by evaporation or the like from the treatedliquid obtained after the treatment, which results in high cost.

The temperature for the treatment depends on the amount of water to beused and may be from about 45° C. to about 250° C., preferably fromabout 60° C. to about 200° C. Under a condition such that the treatmenttemperature is higher than the boiling point of water, it is preferredthat the treatment is conducted under pressure. The period of time forthe treatment is a period enough to hydrolyze the AAH. The higher thetemperature is, the shorter the period of tome is needed. The treatmentmay usually be conducted for about 0.1 hour to about 10 hours, andpreferably about 0.5 hour to about 5 hours.

The water to be used in the water treatment may be added from outside ofthe reaction system. When water exists in an amount needed for the watertreatment in the reaction product to be treated with water or in the AAHobtained after distillation from the reaction product, the water can beutilized for the treatment without adding additional water from outsideof the reaction system.

In the water treatment of the reaction product containing AAH obtainedby the above-described gas phase Beckmann rearrangement reaction method(hydrolysis treatment of AAH), (A) a reaction product containing AAH or(B) an alcohol-removed component obtained after separating alcohol fromthe reaction product containing AAH is used (hereinafter, (A) togetherwith (B) is sometimes referred to as an AAH-containing component).Examples of the method for the water treatment include (1) a method inwhich water is added to the AAH-containing component, heat treatment isconducted and then the product is subjected to purification, (2) amethod in which only AAH is, or a fraction containing a condensed AAH isseparated from the AAH-containing component by fractionation and thelike, and then the obtained AAH or the fraction containing the condensedAAH is treated with water to recover it as ε-caprolactam.

Alternatively, examples of the method for water treatment include (3) amethod in which when alcohol having lower boiling point than that ofwater is used in the gas phase Beckmann rearrangement reaction, water ispreviously added to the rearrangement reaction system, and then therearrangement reaction product containing the water is treated as it isso as to treat AAH therein, or then AAH is treated with water remainingafter allowing alcohol to flow out of the rearrangement reaction productby distillation and other by-products is removed from the resultingproduct by distillation or the like to obtain a product, ε-caprolactam,and (4) a method in which a reaction product obtained by gas phaseBeckman rearrangement reaction is, or a reaction product obtained afterremoving the alcohol out of the reaction product is contacted with waterby extraction using an organic solvent and water as extracting agents,or by crystallization using a solvent containing water, and the like,and removal of other by-products and hydrolysis of AAH are conductedsimultaneously, and the like.

Further, examples of the method for water treatment include (5) a methodin which a reaction product containing AAH of gas phase Beckmannrearrangement reaction is, or a remaining liquid obtained afterpreviously recovering alcohol is dissolved in an organic solvent whichis immiscible with water, and then the resulting solution is allowed tocontact with water, to conduct hydrolysis of AAH and extraction ofε-caprolactam simultaneously so that ε-caprolactam containing no AAH isrecovered, and the like.

It is also possible to combine these methods with known purificationmethods using water such as a method for effecting crystallization usingwater and a method for effecting purification treatment using an aqueouspotassium permanganate solution.

In these hydrolysis methods, it is preferred in the viewpoint ofeasiness in recovering ε-caprolactam to use water in a minimum amountenough to hydrolyze AAH since a large amount of energy is required in aprocess for separating ε-caprolactam from water.

Therefore, a industrially preferable method is as follow:

from a reaction product containing AAH as a impurity obtained by a gasphase Beckmann rearrangement reaction of cyclohexanone oxime using asolid catalyst in the presence of alcohol, the alcohol is substantiallyseparated with distillation or the like beforehand, and the resultingfraction containing AAH is separated and water is added to the fractioncontaining AAH so as to convert the AAH into ε-caprolactam.

It is noted that the previous removal of alcohol is preferred since thehydrolysis of AAH may be suppressed in the presence of much alcohol whenAAH is treated with water, while the explanation of “an alcohol issubstantially separated (or removed) with distillation or the like fromthe reaction product” is used in the present invention. The amount ofalcohol which should be removed is not restricted and varies dependingon an amount of water existing in hydrolysis, treatment temperature orthe like. Alcohol may preferably be removed in an amount of about 90% ormore based on the amount of water existing before the removal.

As described above, the ε-caprolactam of the present invention has lowfree basicity and preferable qualities, since it usually has1-aza-2-alkoxy-1-cycloheptene content of 100 ppm or less, preferably 25ppm or less, more preferably 10 ppm or less. AAH is converted intoε-caprolactam after water treatment and makes the yield of the aimedproduct high and, therefore, industrial available value thereof isextremely high. In addition, the present invention provides a method forproducing ε-caprolactam having a low free basicity with a high yield ofthe aimed product without additional installation of new facilities forseparating or recovering by-products produced by the water treatment,when AAH is separated with distillation or the like from the reactionproduct to obtain a crude caprolactam having a AAH content of 100 ppm orless, the separated AAH is subjected to the hydrolysis treatment andthen the hydrolysis-treated product is recycled and treated in a stepprior to the step of separating AAH. Therefore, the present inventionhas extremely high industrial available values.

EXAMPLE

The present invention is described in more detail by following Examples,which are embodiments thereof and should not be construed as alimitation upon the scope of the present invention.

In the present invention, conversion of cyclohexanone oxime, selectivityto ε-caprolactam and selectivity to AAH were respectively calculatedusing the following formulae:

Conversion of cyclohexanone oxime (%)=[(X−Y)/X]×100

Selectivity to ε-caprolactam (%)=[Z/(X−Y)]×100

Selectivity to AAH (%)=[W/(X−Y)]×100

wherein X, Y and Z respectively represent the followings:

X=molar amount of cyclohexanone oxime supplied

Y=molar amount of cyclohexanone oxime unreacted

Z=molar amount of ε-caprolactam in a product

W=molar amount of AAH in a product

Reference Example 1

0.375 g of a crystalline zeolite-containing catalyst was packed in aquartz reaction tube having an internal diameter of 6 mm φ and a lengthof about 60 cm heated to 370° C. (catalyst layer height: about 23 mm).Raw material liquid having a ratio by weight of cyclohexanoneoxime/methanol/water of 1/1.89/0.052 was introduced into reaction tubeat a rate of 8.54 g/h under nitrogen gas flow of 140 cc/min as a carriergas. The temperature of catalyst layer ( i.e. reaction temperature) was380° C. The resulting reaction product was cooled and collected from theoutlet of the reaction tube in a dry ice/methanol bath. The reactionproduct was analyzed by gas chromatograph. As a result, the conversionof cyclohexanone oxime was 99.4%, the selectivity to ε-caprolactam was96.6%, and the selectivity to 1-aza-2-methoxy-1-cycloheptene(hereinafter, abbreviated as AMH) was 0.82%.

Reference Examples 2 to 4

0.375 g of a crystalline zeolite-containing catalyst was packed in aquartz reaction tube having an internal diameter of 10 mm φ and a lengthof about 60 cm heated to 325° C. (catalyst layer height: about 23 mm).Raw material having a ratio by weight of cyclohexanoneoxime/alcohol/water of 1/1.89/0.052 was introduced at a rate of 8.54 g/hunder nitrogen gas flow of 70 cc/min, and the reaction gas was collectedfrom the outlet of the reaction tube in a dry ice/methanol bath. Thetemperature of the catalyst layer was from 360° C. to 370° C. Thereaction liquid was analyzed by gas chromatograph. The results are shownin Table 1.

Reference Example 5

The procedure was conducted in the same manner as in Reference Examples2 to 4 except that the raw material having a ratio by weight ofcyclohexanone oxime/utilized alcohol/water of 1/5.26/0.052 wasintroduced at a rate of 18.0 g/h to obtain a reaction liquid and thereaction liquid was analyzed by gas chromatograph. The results are shownin Table 1.

TABLE 1 Reference Example 2 3 4 5 Name of alcohol Methanol Ethanoln-Propanol n-Propanol A (molar ratio) 6.4 4.4 3.4 9.3 B (%) 99.73 99.2397.69 87.49 C (%) 95.37 95.78 94.92 94.36 D (%) 0.79 0.32 0.04 0.29Note: A: molar ratio of alcohol/cyclohexanone oxime B: conversion ofcyclohexanone oxime C: selectivity to ε-caprolactam D: selectivity toAAH

Example 1

Into 319 g of reaction liquid obtained by gas phase Beckmannrearrangement reaction (having 15.8% by weight of lactam and 0.19% byweight of AMH, by gas chromatograph analysis) were added 8.50 g of AMHand 6.77 g of water. This reaction liquid was refluxed in afractionation tower packed with about 5-stage glass helipack filler at aref lux ratio of 1 with raising the bath temperature from 80 C to 130°C. over 3 hours, to distill off methanol. The bath was controlled at140° C. at normal pressure, heated for 3 hours, and then, cooled toobtain 88.9 g of a remaining liquid. Gas chromatograph analysis wasconducted to find that lactam content was 63.6% and AMH was notdetected. The production ratio of lactam based on AMH was 74.2%.

It is noted that production ratio of lactam based on AMH and remainingratio of AMH were respectively calculated using the following formulae:

Production ratio of lactam based on AMH(%)=[(B−A)/C]×100

Remaining ratio of AMH (%)=(D/C)×100

A=molar amount of ε-caprolactam in a raw material used for watertreatment

B=molar amount of ε-caprolactam in a product obtained after watertreatment

C=molar amount of AMH in a raw material used for water treatment

D=molar amount of AMH in a product obtained after water treatment

Reference Examples 6 to 9

Hydrolysis of AMH was carried out by treating AMH contained in a lactamcompound with water using one kind of lactam, 2-pyrrolidone rather thanusing ε-caprolactam, in order to accurately investigate a productionyield of ε-caprolactam, which is a product obtained by hydrolysis ofAMH.

2-Pyrrolidone, AMH, water and methanol were used in a ratio by weight of2-pyrrolidone/AMH/water/methanol of 20.0/1.0/1.0/36.6, and heated attemperature for hours shown in Table 2. The reaction product wasanalyzed by gas chromatograph to measure production ratio of lactam andremaining ratio of AMH in the reaction product. The results are shown inTable 2.

Reference Example 10

The procedure was conducted in the same manner as in Reference Examples6 to 8 except that 2-pyrrolidone, AMH and water were used in a ratio byweight of 2-pyrrolidone/AMH/water of 20.0/1.0/1.0, to analyze thereaction product and measure production ratio of ε-caprolactam andremaining ratio of AMH in the reaction product. The results are shown inTable 2.

TABLE 2 No. of Reference Example 6 7 8 9 10 Heating 65° C. × 1 65° C. ×6 45° C. × 3 140° C. × 1 140° C. × 3 temperature × time (hour)Production 4.4 21.1 3.4 65.3 78.9 ratio of lactam (%) Remaining 90.762.6 89.7 3.6 0 ratio of AMH (%)

Example 2

The free basicity of ε-caprolactam containing AMH in an amount shown inTable 3 was measured. The results thereof are shown in Table 3.

Measuring method:

(1) Into a beaker charged with 10.0 g of water, was added a methylred-methylene blue indicator, and the color of the solution was adjustedto grayish blue color (pH 5.70) using an aqueous dilute sodium hydroxidesolution or N/100 normal solution of sulfuric acid while stirring.

(2) 10.00 g of sample, ε-caprolactam, was added and dissolved.

(3) Using the N/100 normal solution of sulfuric acid, was titrated theresulting solution with an automatic buret to obtain an amount ofsulfuric acid used for reaching pH of 5.70 or changing the color of theindicator to grayish blue, which was shown in terms of base equivalentamount per 1 kg of lactam (meq/kg).

TABLE 3 AMH content Free basicity (ppm per lactam) (meq/kg) 0 0.033 1.30.043 2.5 0.054 7.5 0.093 25 0.210 100 0.723

Example 3

0.375 g of a crystalline zeolite-containing catalyst was packed in aquartz reaction tube having an internal diameter of 6 mm φ and a lengthof about 60 cm heated to 370° C. (catalyst layer height: about 23 mm).Raw material having a ratio by weight of cyclohexanoneoxime/methanol/water of 1/1.89/0 was introduced into the reaction tubeat a rate of 8.54 g/h under nitrogen gas flow of 140 cc/min as a carriergas. The temperature of catalyst layer (i.e. reaction temperature) wasfrom 365 to 370° C. The resulting reaction product was cooled andcollected from the outlet of the reaction tube in a dry ice/methanolbath. The reaction product was analyzed by gas chromatograph. As aresult, the conversion of cyclohexanone oxime was 97.3%, the selectivityto ε-caprolactam was 95.2%, and the selectivity to AMH was 1.77%.

100 g of the reaction product was condensed with an evaporator underreduced pressure to obtain 35.1 g of crude lactam. This lactam wasanalyzed with gas chromatograph to find that ε-caprolactam was 92.57%,cyclohexanone oxime was 2.74% and AMH was 1.64% in terms of a percentagearea calculated excluding an area of solvent peak.

Into 30 g of the crude lactam, was added 1.0 g of water. Then theresulting lactam solution was heated at 140° C. for 2 hours in anautoclave. This solution was analyzed with gas chromatograph to findthat ε-caprolactam was 93.82% and oxime was 2.75% in terms of apercentage area calculated excluding an area of solvent peak. AMH wasnot detected.

What is claimed is:
 1. A method for producing ε-caprolactam whichcomprises the step of treating, at a temperature of from 45° C. to 200°C. with water, a reaction product containing1-aza-2-alkoxy-1-cycloheptene, which reaction product is obtained by gasphase Beckmann rearrangement reaction of cyclohexanone oxime using asolid catalyst in the presence of alcohol, to obtain an ε-caprolactamproduct having 100 ppm or less of the 1-aza-2-alkoxy-1-cycloheptene. 2.A method for producing ε-caprolactam which comprises the steps ofseparating a component comprising 1-aza-2-alkoxy-1-cycloheptene from areaction product containing 1-aza-2-alkoxy-1-cycloheptene obtained bygas phase Beckmann rearrangement reaction of cyclohexanone oxime using asolid catalyst in the presence of alcohol, and treating the separatedcomponent comprising 1-aza-2-alkoxy-1-cycloheptene with water at atemperature of from 45° C. to 200° C. to eliminate the1-aza-2-alkoxy-1-cycloheptene from said separated component.
 3. A methodfor producing ε-caprolactam according to claim 1, wherein the reactionproduct to be treated with water is a reaction product obtained bysubstantially separating an alcohol.
 4. A method for producingε-caprolactam according to claim 2, wherein the reaction product to beused for separating the component containing1-aza-2-alkoxy-1-cycloheptene is a reaction product obtained bysubstantially separating an alcohol.
 5. A method for producingε-caprolactam according to any one of claims 1-4, wherein the watertreatment is conducted under a heating condition for a period of time offrom 0.5 to hours.
 6. A method for producing ε-caprolactam according toclaim 2 or 4, wherein the step of separating the component containing1-aza-2-alkoxy-1-cycloheptene from the reaction product is conducted bydistillation treatment.
 7. A method for producing ε-caprolactam, whichcomprises the steps of separating a component containing1-aza-2-alkoxy-1-cycloheptene from a reaction product containing1-aza-2-alkoxy-1-cycloheptene obtained by gas phase Beckmannrearrangement reaction of cyclohexanone oxime using a solid catalyst inthe presence of alcohol, treating the separated component containing1-aza-2-alkoxy-1-cycloheptane with water at a temperature of from 45° C.to 200° C. to convert the 1-aza-2-alkoxy-1-cycloheptene into anε-caprolactam product, and combining the resulting product with said gasphase Beckmann rearrangement reaction product prior to said separationstep.
 8. A method lot producing ε-caprolactam according to claim 7,wherein said component is separated from said reaction product obtainedby gas phase Beckmann rearrangement from which alcohol has beensubstantially removed.
 9. A method according to any one of claims 1-4, 7or 8 for producing ε-caprolactam obtained by gas phase Beckmanrearrangement reaction of cyclohexanone oxime using a solid catalyst inthe presence of alcohol, which comprises the step of treating by-product1-aza-2-alkoxy-1-cycloheptene with water so that a1-aza-2-alkoxy-1-cycloheptene content in the resulting ε-caprolactam is25 ppm or less.
 10. A method according to any one of claims 1-4, 7 or 8for producing ε-caprolactam obtained by gas phase Beckmann rearrangementreaction of cyclohexanone oxime using a solid catalyst in the presenceof alcohol, which comprises the step of treating by-product1-aza-2-alkoxy-1-cycloheptene with water so that a1-aza-2-alkoxy-1-cycloheptene content in the resulting ε-caprolactam is10 ppm or less.
 11. A method for producing ε-caprolactam according toany one of claims 1-4, 7 or 8, wherein the amount of water to be usedfor the treatment is from about 3 equivalent to about 30 equivalent tothe amount of 1-aza-2-alkoxy-1-cycloheptene.
 12. A method for producingε-caprolactam according to any one of claims 1-4, 7, or 8, wherein theamount of water to be used for the treatment is from about 3 equivalentto 14.4 equivalent to the amount of 1-aza-2-alkoxy-1-cycloheptene.